Battery systems often include monitoring devices that measure the high voltage isolation resistance in a battery pack. FIG. 1 depicts a schematic diagram of a prior-art measurement circuit. In FIG. 1 isolation resistance in the resistor RLeg is identified using the following equation:
      R    Leg    =                              V          pack                -                              (                                          R                ⁢                                                                  ⁢                1                            +                              R                ⁢                                                                  ⁢                2                                      )                    *                                    (                              Va                +                Vb                            )                                      R              ⁢                                                          ⁢              1                                                            Va          +          Vb                          R          ⁢                                          ⁢          1                      .  The resistance RLeg is equivalent to the isolation resistance (RISOBatt) of the battery. FIG. 1 depicts a circuit with two switches, where a first switch is connected in a + line and a second switch is connected in the − line. The isolation resistance refers to a resistance between the battery and electrical ground and is often referenced in terms of ohms per volt. Existing high-voltage systems use mechanical relays or photo-MOS (solid state relay) switches.
In high-voltage battery systems, the switching hardware that is required to operate the prior art monitoring circuit adds to the expense and complexity of the battery system. Consequently, alternative monitoring circuits that measure the isolation resistance RISOBatt without requiring additional high-voltage components specifically for the purpose of measuring isolation resistance would be beneficial.